Conclusions

Common-azimuth migration produced better results in the subsalt than a single-arrival Kirchhoff migration. The subsalt reflectors are much more interpretable in the common-azimuth images than in the Kirchhoff images, both because the images are devoid of the typical subsalt Kirchhoff artifacts and because the reflectors themselves are better imaged.

Although superior to Kirchhoff images, the common-azimuth images in the subsalt are far from perfect. Sub-optimal images are probably caused by a combination of poor reflectors' illumination and inaccuracies in the migration procedure. The shortcomings in the migration procedure are of two types: common-azimuth approximations and numerical approximations. We plan to address both types. We are developing a narrow-azimuth extension to common-azimuth migration Vaillant and Biondi (1999). And we plan to apply to common-azimuth downward continuation more accurate numerical methods that are based on a combination of the helix Rickett et al. (1998) and Ristow's Fourier finite-difference methods Ristow and Ruhl (1994).